One of my bucket list items is to learn how to build stereo equipment. I am needing help in translating a schematic into a drawing I can understand. I have attached a schematic of a simple amp and would be greatly appreciative if someone could translate the schematic into a layout drawing. This will help me to learn how to interrupt a schematic and also the ability to have a drawing to build the amp. ANY HELP WOULD BE GREATLY APPRECIATED. Here is the schematic. THANKS FOR YOUR WILLINGNESS TO CONSIDER TO HELP.
DIY Single-Ended (SE) KT88 / 6L6 / EL34 / 6CA7 Tube Amplifier
Thanks Greg
DIY Single-Ended (SE) KT88 / 6L6 / EL34 / 6CA7 Tube Amplifier
Thanks Greg
Here's a shortcut to explaining what-all the components do.
(1) is the volume control potentiometer (variable resistor). It is special in that it does not have a linear relationship between how far the knob is turned and the proportion of resistance measured at the tap (arrow). Instead, it has a "analog taper", which causes the relative volume change to be much more linear sounding. Its ironic, but math supports the idea.
(2) Vacuum tubes like most amplifying devices, transform changes in potential on their grids to changes in the flow of current through them. Hence why they're called "valves". You twist (volts) a valve, and it in turn regulates the flow of water (current) through the pipe. But since the next stage needs voltage for its grid, the current has to be turned into volts. Resistors do that really well.
Ohms law Volts = Amps (times) Ohms or E = IR is the key. Current flowing through the resistor becomes a voltage (what we want).
(3) But… the grid needs to be a bit negative relative to the source of electrons (the cathode, or bottom terminal). There is one obvious way to do that (use a battery to make the grid negative, or a power supply) … and this non-obvious-to-newbies method: remembering that E = IR, if there is some nominal current I flowing thru the cathode resistor (1 kΩ), then there will be a voltage across it. Ignoring the cap, that voltage raises the cathode some number of volts.
RAISING the cathode "puts the grid relatively negative" with respect to it! Now all would be swell, except for the fact that as signal is imposed on the tube, it will cause a varying of current thru the tube (what we want!), but which also causes varying of the 'cathode raising voltage' afforded by the 1 kΩ resistor. How to avoid that?
BYPASSING the cathode resistor with a capacitor, which in essence makes a tiny DC power supply that counters the signal. The bias point remains relatively constant, with it being more constant with larger bypass capacitors. 100 μF is pretty large. But not crazy.
(4) & (5) The problem with most high-volt supplies is that they carry a fair amount of hum and "ripple" from the power supply design. Some don't, but many do. By sending the high-volt supply ("B+") thru an inductor (which squashes the high frequency 'buzz' component) and also a capacitor (squashes some of the low frequency “hum” component) … we get "squashed buzz'n'hum"
This is good to feed to the first stage's anode resistor. Keep that hum out!
(6) is the connection to the power supply high voltage output positive leg.
(7) Even though the 47 kΩ anode (voltage converter) resistor is doing a fine job, it (the designer) has to leave quite a bit of positive voltage on the anode of the tube. It needs volts to work. Gotta have 'em. But the next stage grid wants to be ”basically at ground“, just like the first stage. How to do this?
Use a capacitor in its other fashion (not as power storage but) as a DC blocking device. It readily lets A/C ("the signal") get thru, but blocks the average DC voltage on the anode of the first tube. Great!
(8) Here is the resistor that ties the grid to ground, or "0.0" volts. It is a largish resistor, meaning that it is a ”light load“ on the A/C (signal) part coming thru the capacitor. Thus it does its job without unduly draining the gain of the previous stage.
(9) again, like (3) … the grid (at about 0 volts) wants to be relatively negative compared to the cathode. The "easy way" is to stick a resistor between cathode and ground, and let E = IR produce a positive voltage. The cathode goes positive, making the grid relatively negative, and all's well in Denmark. The capacitor (again) is used to turn to bypass the A/C (or signal) component around the resistor, making the tube see the resistor's positive voltage more like a power supply than a resistor.
(10) The "triode selector" is a two-way switch, with one position tying the 2nd grid of the output tube to the plate (anode). In so doing, the power tube will have curves and responses more or less like a classic single grid triode. You'll get a certain sound out of that.
(11) The ultralinear tap (flipping switch other way) ties the 2nd grid of the output tube to the transformer's UL tap. This drives the tube into a more "2 grid type tube" mode of operation. You'll get a different sound (and gain).
(12) Here Be The Transformer which turns the large-voltage-swing, but small-current-capability output of the tube into small-voltage-swing, but large-current capability output suitable for modern speakers. The COM is "common", and the "8" is for an 8 Ω speaker cabinet.
YOU NEED NO MORE knowledge of this particular circuit to more or less understand it. But you do need math if you wish to abstract it, and start designing your own. You need the "tube specs" which are series' of graphs and tables of not-to-exceed operating points. You need to bone up on a whole variety of designs other than this one … for the topologies vary quite a bit.
And most of all, you NEED to cobble one of these together. Really!
Its the best way to learn.
But BEWARE the voltages involved.
They can kill in an instant.
And man … that permanently upsets the applecart.
GoatGuy
(1) is the volume control potentiometer (variable resistor). It is special in that it does not have a linear relationship between how far the knob is turned and the proportion of resistance measured at the tap (arrow). Instead, it has a "analog taper", which causes the relative volume change to be much more linear sounding. Its ironic, but math supports the idea.
(2) Vacuum tubes like most amplifying devices, transform changes in potential on their grids to changes in the flow of current through them. Hence why they're called "valves". You twist (volts) a valve, and it in turn regulates the flow of water (current) through the pipe. But since the next stage needs voltage for its grid, the current has to be turned into volts. Resistors do that really well.
Ohms law Volts = Amps (times) Ohms or E = IR is the key. Current flowing through the resistor becomes a voltage (what we want).
(3) But… the grid needs to be a bit negative relative to the source of electrons (the cathode, or bottom terminal). There is one obvious way to do that (use a battery to make the grid negative, or a power supply) … and this non-obvious-to-newbies method: remembering that E = IR, if there is some nominal current I flowing thru the cathode resistor (1 kΩ), then there will be a voltage across it. Ignoring the cap, that voltage raises the cathode some number of volts.
RAISING the cathode "puts the grid relatively negative" with respect to it! Now all would be swell, except for the fact that as signal is imposed on the tube, it will cause a varying of current thru the tube (what we want!), but which also causes varying of the 'cathode raising voltage' afforded by the 1 kΩ resistor. How to avoid that?
BYPASSING the cathode resistor with a capacitor, which in essence makes a tiny DC power supply that counters the signal. The bias point remains relatively constant, with it being more constant with larger bypass capacitors. 100 μF is pretty large. But not crazy.
(4) & (5) The problem with most high-volt supplies is that they carry a fair amount of hum and "ripple" from the power supply design. Some don't, but many do. By sending the high-volt supply ("B+") thru an inductor (which squashes the high frequency 'buzz' component) and also a capacitor (squashes some of the low frequency “hum” component) … we get "squashed buzz'n'hum"
This is good to feed to the first stage's anode resistor. Keep that hum out!
(6) is the connection to the power supply high voltage output positive leg.
(7) Even though the 47 kΩ anode (voltage converter) resistor is doing a fine job, it (the designer) has to leave quite a bit of positive voltage on the anode of the tube. It needs volts to work. Gotta have 'em. But the next stage grid wants to be ”basically at ground“, just like the first stage. How to do this?
Use a capacitor in its other fashion (not as power storage but) as a DC blocking device. It readily lets A/C ("the signal") get thru, but blocks the average DC voltage on the anode of the first tube. Great!
(8) Here is the resistor that ties the grid to ground, or "0.0" volts. It is a largish resistor, meaning that it is a ”light load“ on the A/C (signal) part coming thru the capacitor. Thus it does its job without unduly draining the gain of the previous stage.
(9) again, like (3) … the grid (at about 0 volts) wants to be relatively negative compared to the cathode. The "easy way" is to stick a resistor between cathode and ground, and let E = IR produce a positive voltage. The cathode goes positive, making the grid relatively negative, and all's well in Denmark. The capacitor (again) is used to turn to bypass the A/C (or signal) component around the resistor, making the tube see the resistor's positive voltage more like a power supply than a resistor.
(10) The "triode selector" is a two-way switch, with one position tying the 2nd grid of the output tube to the plate (anode). In so doing, the power tube will have curves and responses more or less like a classic single grid triode. You'll get a certain sound out of that.
(11) The ultralinear tap (flipping switch other way) ties the 2nd grid of the output tube to the transformer's UL tap. This drives the tube into a more "2 grid type tube" mode of operation. You'll get a different sound (and gain).
(12) Here Be The Transformer which turns the large-voltage-swing, but small-current-capability output of the tube into small-voltage-swing, but large-current capability output suitable for modern speakers. The COM is "common", and the "8" is for an 8 Ω speaker cabinet.
YOU NEED NO MORE knowledge of this particular circuit to more or less understand it. But you do need math if you wish to abstract it, and start designing your own. You need the "tube specs" which are series' of graphs and tables of not-to-exceed operating points. You need to bone up on a whole variety of designs other than this one … for the topologies vary quite a bit.
And most of all, you NEED to cobble one of these together. Really!
Its the best way to learn.
But BEWARE the voltages involved.
They can kill in an instant.
And man … that permanently upsets the applecart.
GoatGuy
Attachments
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I'd recommend for a first build that you leave out the 'triode option switch' (10). Just wire in that 100R resistor from the KT88 screen grid to plate (and forget the switch).
The reasons?
1) Who needs the complexity? One less thing to worry about, and it's unnecessary because...
2) The damping factor with the tube's screen grid connected to the screen tap on the output transformer will be worse than if the tube is wired triode. That means the bass will sound tubbier with the screen tap than in triode mode, especially with most contemporary bookshelf-type speakers.
If you really want to add that screen tap, you'll also want to add a negative feedback loop. That would add more complexity.
Just a suggestion, no worries...
The reasons?
1) Who needs the complexity? One less thing to worry about, and it's unnecessary because...
2) The damping factor with the tube's screen grid connected to the screen tap on the output transformer will be worse than if the tube is wired triode. That means the bass will sound tubbier with the screen tap than in triode mode, especially with most contemporary bookshelf-type speakers.
If you really want to add that screen tap, you'll also want to add a negative feedback loop. That would add more complexity.
Just a suggestion, no worries...
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The whole point of a schematic is that it is easier to understand than a layout diagram. It omits layout details so we can concentrate on what is connected to what. A layout diagram may help with constructing a circuit, but it makes understanding it much harder. That is why we often on here ask a newbie to provide a schematic when he asks us to debug a layout diagram.Taipan said:
You can build an amp without a schematic, but you need a schematic in order to understand it.
Goatguy's post here is the best thing I've ever read on the Internet, at least regarding tube stuff. Thanks for the fun read!
Thank You
Thank you to everyone for their comments and help. I particularly want to thank GoatGuy for his detailed message and marked up drawing. I also want to thank Rongon, DF96 and RET for their comments. All the help is appreciated.
Thank you to everyone for their comments and help. I particularly want to thank GoatGuy for his detailed message and marked up drawing. I also want to thank Rongon, DF96 and RET for their comments. All the help is appreciated.
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